Bonds may be issued to an amount not exceeding the amount of liens assessed for the cost of improvements to be paid by special assessment.

After the equalization, approval and confirmation of the levying of the special assessments for improvements as provided by s. 170.08 and as soon as a contract for said improvement has been finally let, the governing authority of the municipality may by resolution or ordinance authorize the issuance of bonds, to be designated “Improvement bonds, series No. ________ ,” in an amount not in excess of the aggregate amount of said liens levied for such improvements. Said bonds shall be payable from a special and separate fund, to be known as the “Improvement fund, series No. ________ ,” which shall be used solely for the payment of the principal and interest of said “Improvement bonds, series No. ________ ” and for no other purpose. Said fund shall be deposited in a separate bank account; and all the proceeds collected by the city from the principal, interest, and penalties of said liens shall be deposited and held in said fund. Said bonds so issued shall never exceed the amount of liens assessed, and said bonds shall mature not later than 2 years after the maturity of the last installment of said liens. Said bonds shall bear certificates signed by the clerk of the municipality certifying that the amount of liens levied, the proceeds of which are pledged to the payment of said bonds, are equal to the amount of the bonds issued. The bonds may be delivered to the contractor in payment for his or her work or may be sold at public or private sale for not less than 95 percent of par and accrued interest, the proceeds to be used in paying for the cost of the work. Said bonds shall not be a general obligation of the city, but shall be payable solely out of said assessments, installments, interest, penalties, provided that said bonds may be secured by any other revenues that may be legally available for such purpose. Any surplus remaining after payment of all bonds and interest thereon shall revert to the city and be used for any municipal purpose. Bonds issued under this section may be refunded from time to time as provided in this section.